Staple fibers and processes for making same

ABSTRACT

Improved staple fibers and processes for producing them are provided. The processes are particularly useful for forming staple fibers from poly(trimethylene terephthalate), especially carpet staple fibers. The processes include prewetting undrawn yarns and drawing the fibers under wet and warm conditions, thermo-fixing the texture, and drying at relatively low temperatures. Fibers produced according to the processes disclosed herein have improved properties and reduced brittleness as compared to fibers prepared using conventional processes.

FIELD OF THE INVENTION

The present invention relates to staple fibers and processes forproducing them. The processes are particularly useful for producingfiber from poly(trimethylene terephthalate), especially carpet staple.The processes allow the production of staple yarns from aged, undrawnfiber.

BACKGROUND

Polyalkylene terephthalates such as polyethylene terephthalate (“2GT”)are common commercial polyesters. They have excellent physical andchemical properties, including chemical, heat and light stability, highmelting point and high strength. As a result they have been widely usedfor resins, films, and fibers.

A key difference between drawing nylon and PET fiber lies in thetemperature to which the undrawn yarn is raised to allow the fibers tostart drawing in a uniform manner with a reasonable draw force. Nylonand PET can be drawn at room temperature but are best drawn at atemperature above their glass transition temperatures of about 40° C.and 65° C. respectively to obtain uniform physical properties and/orpreclude undue filament breakage during drawing. The glass transitiontemperature (T_(g)), also called the second order transitiontemperature, can be obtained by dilatometric methods. The undrawn yarncan be raised to above its T_(g) before drawing with draw assists suchas heated rolls.

The making of polyester and nylon staple fibers often involves amulti-stage process. In the first step, polymer is extruded intofilaments, which are quenched, attenuated, and lubricated; and thefilaments of each spin position are combined into a filament bundle.Filament bundles from the individual spin positions are then immediatelycombined at the spinning wall into a spun rope. Drawing of the spun ropeto form an oriented structure having useful properties is often done ina separate step, wherein the spun rope is piddled into a can forsubsequent drawing and texturing. The spun cans are assembled into acreel of economic size, for drawing at the drawing machine. In thissplit spin/draw staple process, there is an inherent time delay betweenthe extrusion and drawing process to allow for producing such a creelfor drawing. This delay is often substantial and depends, in part, onthe number of spin positions and spin rate of the spinning machine.Further, production schedules can extend the delay before drawing todays rather than hours.

After the fiber is drawn to give it adequate strength for downstreamprocessing and end use, it is textured and lubricated to provideappropriate fiber friction and value. A stuffing box crimper usuallycarries out the nylon and PET staple texturing. The crimping equipmentand process conditions can impact the type, frequency, and permanence ofthe crimp. The crimped tow can be pre- or post treated with lubricants,dried, relaxed or annealed, and cut into staple fibers and baled. Theoperations from drawing to baling can be carried out in separate stepsor in a coupled process. The optimum conditions depend on the fibercomposition and end use, and the cut length depends on end use andstaple processing system i.e. cotton, wool, modified worsted. The cottonsystem equipment generally uses short fibers (1-3 inches) for textileapplications and the modified worsted system, used for carpetprocessing, uses longer fibers (6-8 inches).

Bales of the cut staple fibers are converted into a continuous yarn in amulti-stage mill operation-using opening, blending, carding, drafting,and spinning equipment. Certain physical properties are highly desirablein the fibers so that they can undergo the drawing and texturingprocesses without diminished quality in the resulting fiber. One of themost critical parameters is crimp frequency (crimps per inch, c.p.i) andits permanence (crimp take-up, CTU). It is desirable that the staplefibers have enough crimp to provide adequate sliver cohesion but not toomuch to cause excessive fiber entanglement in operations such asblending. The crimp should be permanent enough to withstand theconsiderable forces in mill processing. For example, when such fibersare carded to comb them to parallelism, they can, because ofentanglement, be snarled into defects or stretched until crimp ispermanently removed or the filaments break. Also if the crimp is lost,either from stretching or due to insufficient permanence, the sliverleaving the card can have insufficient strength and cohesion and couldbreak and prevent further operation. Even though the CTU is increasedwith crimp frequency, it is desired that the fiber have a balance ofcrimp frequency and CTU to prevent excessive entanglement from too highcrimp. Carpet fibers have higher denier than textile fibers and arestiffer so they require lower crimp levels to prevent entanglement. Inaddition, any crimp loss reduces the bulk of the yarn, which reduces thevalue of the carpet. Lower yarn bulk provides less cover and so requiresmore weight for equal cover. Processing lubricants are applied to helpcontrol fiber-to-fiber and fiber-to-metal friction, and provide staticprotection. In carpet production, the spun yarns are typically plied,heatset to set the twist, tufted into a primary backing, and dyed. Then,a secondary backing is applied to the primary backing, using a latexadhesive, which locks in the tufts and provides dimensional stability tothe carpet.

Poly(trimethylene terephthalate), also referred to as PTT or 3GT is apolyester suitable for use in carpet, textile, and other thermoplasticresin applications. Poly(trimethylene terephthalate) in fiber form isdesired because it can be dyed at atmospheric pressure with dispersedyes, has a relatively low bending modulus, a relatively high elasticrecovery and resilience, and resistance to staining. However, undrawnPTT yarns, under some spinning conditions can become brittle upon aging(e.g., storage). Conventional two-step processes used for makingpolyester staple fibers, as mentioned hereinabove, include an inherenttime delay between the extrusion and drawing process, which effectivelyages the fibers. Brittle fibers can be difficult to draw and may even beundrawable.

U.S. Pat. No. 6,109,015 discloses an attempt to overcome the problem ofbrittleness in PTT. The patent discloses a continuous process forproducing PTT yarn stated to have improved wear over yarns made inconventional two stage processes. The continuous process avoids theaging of the fiber by eliminating the storage step by coupling the spinand draw steps. However, the process also requires major equipmentmodifications, which prevents the use of existing conventional two-stepequipment.

Other efforts to overcome problems associated with aging of undrawnyarns were directed to reduction or control of shrinkage. For example,Patent Publication No. WO 01/68962 A2 discloses a two-step process forproducing fine denier textile yarns from poly(trimethyeleneterephthalate) on equipment with relatively long quench zones. The firststep produces undrawn yarn, and the second step converts the undrawnyarn to a staple fiber. The process includes preconditioning the fiberunder tension at a temperature of 60° C. or above, then drawing thefiber, at a temperature of 60° C. or above, preferably to 80-85% of thetotal draw length of the fiber. After an optional second drawing stage,the fiber is relaxed at a temperature of up to 190° C.

In certain textile end uses, staple fibers are preferred over continuousfilament. Examples include staple spun yarns for apparel fabrics (1-6dpf) and carpet (6-25 dpf) both of which require discontinuous fiberrather than continuous to permit use of textile staple processingequipment. The manufacture of staple fiber suitable for fabrics andcarpets can present special problems, particularly in conventional splitspin/draw processes where the drawing is carried out in a separate step.A need thus remains for processes for manufacturing fiber, andparticularly staple fiber, from PTT.

SUMMARY OF THE INVENTION

The present invention provides processes for forming staple fiber fromPTT fibers. In particular, the processes disclosed herein include stepsof drawing, crimping, and drying. PTT fibers produced according to theprocesses disclosed herein are particularly suitable for use as carpetyarns. The processes are suitable for processing undrawn yarn (“UDY”),including aged undrawn yarn, which is generally stored for some timebefore being drawn in a split spin/draw process, and can be too brittleto be drawn in a conventional manner using conventional equipment. Theprocesses disclosed herein allow the processing of undrawn PTT yarnsinto staple fibers with little or no brittleness due to fiber agingduring storage and/or processing of the undrawn yarn. Another advantageis that conventional nylon or PET equipment can be simply modified toproduce the improved fiber. The PTT fibers can be melt spun in aconventional manner.

One aspect of the present invention is a process for making an improved6 to 25 dpf staple fiber consisting essentially of poly(trimethyleneterephthalate). Such staple fibers are commonly used in carpetapplications. For example, carpet fibers can be about 10, 15, or 20 dpf.However, it is contemplated that the processes of the invention areuseful in making fibers of all deniers within the recited ranges. Theprocess includes: prewetting an undrawn yarn at a temperature less thanabout 45° C., more preferably less than about 40° C., and even morepreferably at about 25° C.; drawing the fiber under wet conditions at atemperature from about 45° C. to about 95° C. in a first stage to about30-90 percent of its final length; drawing the fiber in a second stageat a temperature from about 60° C. to about 98° C. under wet conditions;crimping the drawn fiber; thermo-fixing the crimped fiber with steam ata temperature from about 80 to about 100° C., preferably at about 85°;and drying and relaxing the fiber. Preferably, the fiber is drawn at atemperature of about 50° C. in the first stage and at a temperature ofabout 60° C. in the second stage, and the crimped fiber is dried at atemperature from about 60° C. to about 120° C. Wet conditions can be,for example, in the presence of water and/or steam, such as under wateror under an aqueous solution of processing finish. Preferably, theundrawn yarn is prewet and drawn in a manner that exposes the maximumfiber area practical to the wetting medium to insure the most uniformtreatment.

These and other embodiments will be apparent to those skilled in theart, in view of the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of exemplary equipment used in aprocess according to the invention for making fiber frompoly(trimethylene terephthalate).

DETAILED DESCRIPTION

Unless otherwise stated, the following terms when used herein have thefollowing definitions. Measurements reported herein are reported usingconventional U.S. textile units, including denier, which is a metricunit. Specific properties of the fibers were measured as describedbelow. When available, definitions hereinbelow were taken from TheMan-Made Fiber and Textile Dictionary, Fourth Edition, Reprinted 1986,Celanese Corporation, which is incorporated herein by reference in itsentirety.

Where a range of numerical values is recited herein, unless otherwisestated, the range is intended to include the endpoints thereof, and allintegers and fractions within the range. It is not intended that thescope of the invention be limited to the specific values recited whendefining a range. Moreover, all ranges set forth herein are intended toinclude not only the particular ranges specifically described, but alsoany combination of values therein, including the minimum and maximumvalues recited.

“Staple” refers to either natural fibers or cut lengths from filaments.The term staple (fiber) is used in the textile industry to distinguishnatural or cut man-made fibers from filament. Man-made fibers are cut toa specific length, for example, as long as 8 inches or as short as 1.5inches or less, so they can be processed on cotton, woolen, or worstedyarn spinning systems, or flocked.

“Relative viscosity”, also called “laboratory relative viscosity” (LRV)is the viscosity of a polymer dissolved in hexafluoroisopropanolcontaining 100 ppm of 98% reagent grade sulfuric acid (HFIP solution).The viscosity measuring apparatus is a capillary viscometer obtainablefrom a number of commercial vendors (for example, Design Scientific,Cannon). The relative viscosity in centistokes is measured on a 4.75 wt.% solution of polymer in HFIP solution at 25° C. as compared with theviscosity of pure HFIP solution at 25° C.

“Quench zone” is used herein with regard to equipment for processing PTTfibers to refer to the cooling distance from the spinneret from whichpolymer is extruded to make a spun fiber, to the roll that is used toforward the spun fiber at draw-off speed to cans for subsequent drawing.

A “draw creel” is a framework arranged to guide the ends from a numberof containers (cans) so that many ends can be withdrawn smoothly andevenly without tangling and be forwarded into a draw machine (beam). Acreel stock is the aggregate of the supply UDY cans to be drawn at onetime.

“Undrawn yarn” is a term customarily applied to fiber that has not beendrawn, and is not intended herein to include fibers that have been drawnand processed into a yarn product, such as those yarns used in knittingor weaving fabric. After melt spinning, undrawn yarn is accumulateduntil an appropriate total denier for the draw machine is produced.Accumulation can take up to 24 hours or more including dormant orstorage time between steps. For example, making sufficient undrawn yarnfor economic drawing at the draw line generally takes 6 hours or more.Due to production scheduling and other practical considerations, fibermay be stored for several days. Fiber having been exposed to suchstorage time is referred to as “aged” or “aged undrawn yarn”.

“Draw ratio”, or “draw down”, is the amount by which filaments arestretched following melt spinning. As used herein, “draw ratio” refersto machine draw ratio, which is the ratio of the surface speed of thepulling rolls to the forwarding rolls (rolls that move the fiber). As aresult of pulling some stretching occurs.

“Modification Ratio” (MR) refers to the shape of a trilobal filament. Itis the ratio of the circumscribed or outer diameter of the filamentlobes divided by the inscribed diameter or diameter of the core. It canbe measured using transparent calibrated templates or digital imagingmethods. The higher the number, the longer are the three lobes of thetrilobal filament.

“Crimp” is the texture or waviness of a fiber expressed as crimps perunit length. Crimp frequency, reported in crimps per inch (cpi), is anindirect measure of yarn bulk. Crimp frequency is measured in thefollowing manner. A filament is placed between two clamps, and then atension of 2 mg/denier is applied to the filament. The number of crimpsbetween the clamps is counted. Next a 50 mg/denier tension is appliedand the extended length is recorded. The process is repeated until tenfilaments have been measured. The results are averaged, and from theaveraged results the cpi is calculated as follows: CPI=(number of crimpsin filament)/(extended length).

“Tow” is a large strand of continuous man-made fiber filaments withoutdefinite twist collected in loose, rope-like form, usually held togetherby crimp. Tow is the form the fiber reaches before being cut intostaple.

“Final length”, as used herein in reference to drawn fibers, refers tothe total length to which a fiber is drawn.

“Crimp Take-Up” (CTU, %) is a measure of fiber's resilience. CTUindicates how well a specified frequency and amplitude of the secondarycrimp is set in the fiber. CTU relates the length of the crimped fiberto the extended fiber and thus it is influenced by crimp amplitude,crimp frequency, and the ability of the crimps to resist deformation.Crimp take-up can be calculated using the formula:

CTU(%)=100(L ₁ −L ₂)/L ₁

wherein L₁ represents the extended length (fibers hanging under an addedload of 0.13_(—)+0.02 gpd for a period of 30 seconds), and L₂ representsthe crimped length (length of the same fibers hanging under no addedweight after resting for 60 seconds after the first extension.

“Carding” is a process whereby staple is aligned and formed into acontinuous untwisted strand called sliver. The card machine consists ofa series of rolls whose surfaces are covered with many projecting metalteeth.

A “sliver” is a continuous strand of loosely assembled fibers withouttwist. Sliver is delivered by the card or drawing frame. The productionof sliver is the first step in the textile operation that convertsstaple fiber into a form that can be drawn and eventually twisted into aspun yarn.

“Sliver tenacity” is defined as the weight needed to break a sliverdivided by the sliver weight. The strength or cohesion of fibers can bemeasured by a sliver tenacity test and is helpful in determining theperformance of fibers in textile processing. For example, the sliverdesirably has sufficient cohesion that it does not break as it is beingforwarded in the carding or drafting operation. To measure slivertenacity, a length of sliver is taped at one end and the opposite(untapped) end is placed in a clamp. Weights are then successivelyplaced on the taped end of the sample in 10 second intervals until thesliver breaks. Sliver tenacity=weight to break (grams)/sliver weight(grains).

“Bulked yarn” is a qualitative term to describe a textured yarn. “Carpetbulk” is carpet pile weight, relative to other fibers, for equivalentsubstance (resistance to compression) and cover. It can be measured withvarious compression instruments. In the present Examples, carpet bulkwas assessed based on subjective comparative tests by a panel of carpetexperts.

Twisting is the process of combining filaments into a textile yarn on aspinning frame. “Twist” is the number of turns about its axis per unitlength of a textile yarn. Twist can be expressed as turns per inch(tpi).

The “gauge” (ga.) is the distance in inches between needles on a carpettufting machine.

The present invention provides improved processes for forming fibersfrom PTT. The processes include prewetting quenched undrawn yarnpreferably at temperatures below the T_(g) of the yarn, and drawingquenched, undrawn PTT yarn filaments at temperatures preferably abovetheir T_(g) and under wet conditions, e.g., in the presence of waterand/or steam.

The present inventors have found that if PTT undrawn yarn is processedusing conventional melt spun processes known for producing nylon carpetfiber, the fiber exhibits extreme brittleness within a short time afterextrusion. The brittleness results in a weak fiber that can be easilysnapped even under low tension. The surprising structure changes overtime, which do not occur with PET polyester or nylon, prevent orinterfere with subsequent drawing intended to orient the structure andgive it useful strength. Also, after drawing, when some conventionalprocesses known for use with certain other fibers are used for formingPTT staple fibers, there can be severe fiber crimp loss and henceinsufficient sliver cohesion for downstream mill processing such ascarding. Prevention of insufficient sliver cohesion and attaining highcarpet bulk is desirable. It is also desirable for economic reasons tobe able to use conventional nylon or polyester equipment for theproduction of PTT staple.

In preferred embodiments, standard equipment such as that conventionallyused in making yarn from PET or nylon can be used in the processesdisclosed herein. An exemplary preferred embodiment is illustratedschematically in FIG. 1. Undrawn yarn (“UDY”) 1, having been spun andpassed through the quench zone (not shown), enters prefeed dip tank 2and is forwarded by rolls 3 and 4 and wetted under water (water levelnot shown). Wetted UDY 1′ is forwarded by rolls 5, 6, 7, 8, and 10, thenenters first drawing stage (“Draw 1”) in dip tank 9 and is partiallydrawn between rolls 10 and 11 under water in first stage dip tank 9. Theyarn is partially drawn by rolls 11, 12, 13, 14, 15, and 16, which aredriven at a faster speed than roll 10. The partially drawn yarn 1″ isthen rewetted by water spray jets 17. Optionally, a steam jet or anotherdip tank can be used in place of water spray jets. Further drawing(“Draw 2”) is achieved by rolls 18, 19, 20, and 21, and puller rolls 22and 23, which are driven at a faster speed than roll 16. Nip rolls 5′,8′, 14′, 22′ and 25′ are used to minimize yarn slippage. After the yarnhas gone through the second drawing stage, finish sprayer 24 applies adilute processing finish to the drawn yarn 1′″, which is then forwardedand maintained under tension by puller rolls 25 and 26, until it isforced into stuffer box crimper 27 by driven crimper nip rolls 26′,where it is crimped and thermofixed by application of steam at 28. Thecrimped yarn 1′″, called “tow”, is then forwarded in a relaxed statethrough a conventional belt dryer 29, cut by rotary cutter 30 and baled31 for storage and shipping.

The processes disclosed herein provide not only the ability to drawaged, brittle PTT undrawn yarn, but also provide fiber having improvedphysical properties. The processes also provide fiber having improvedsliver cohesion after carding and improved bulk as compared to fibersdrawn using conventional processes. The processes are preferably used todraw 5-60 dpf undrawn yarn. Fibers prepared according to the processesdisclosed herein thus provide a balance of physical properties, millprocessibility, and carpet bulk. The processes can also be carried outby modifying equipment designed for production of either nylon or 2GTpolyester staple.

In the processes disclosed herein, prior to being drawn, PTT fiber,produced by conventional melt spinning, is prewet to improve temperatureuniformity throughout the fiber prior to the carrying out of furtherprocessing steps. Prewetting can be carried out in a dip tank. Thetemperature of the dip tank is preferably below about 45° C., morepreferably less than about 25° C. if the fiber is under tension. If theprewetting is carried out a temperature close to the glass transition ofthe polymer, it is desirable to control the tension on the fiber toprevent uneven drawing of the fiber before the drawing stage.

In a preferred embodiment, after wetting, the fiber is drawn in at leasttwo stages. In a first stage, the fiber is drawn, with the fiber beingmaintained at a temperature of at least about 45° C. and not higher thanabout 95° C. Preferably, the temperature is about 80° C. or less, morepreferably about 70° C. or less, even more preferably about 60° C. orless. Even more preferably, the first drawing stage is carried out at atemperature from about 50° C. to about 55° C. The temperature of thefiber during the drawing stages is not necessarily equivalent to theambient temperature, as the fiber can be drawn in steam, which has atemperature of 100° C. or more.

In the first drawing stage, for fiber suitable for use in carpet, thefiber is drawn to at least about 30 percent of its final length,preferably at least about 40 percent, and more preferably to about 50percent of its final length. Also, the fiber is drawn to about 90percent of its final length or less, preferably about a 70 percent orless, and more preferably about 55 percent or less. For finer deniertextile fibers, it is preferred that a higher proportion of the totaldraw be carried out in the first draw stage than for higher denierfibers.

In the first drawing stage, the fiber is drawn under wet conditions.“Under wet conditions” is a term readily understood by persons ofordinary skill in the art and includes, for example, under water, undera spray, and in a humid environment. In highly preferred embodiments,the fiber is drawn under water or an aqueous solution of processingfinish also referred to as “dilute finish.” Even more preferably, thefiber is drawn under water as a spun rope that is spread into a band aswide as practical, preferably controlling the thickness of the band andmaintaining it as wide as possible, to permit uniform wetting andheating, at about 50° C. and to about 55% of the final draw length. Thespun rope can be substantially rectangular in shape. It is highlypreferred that the spun rope have a transverse thickness less than about300,000 denier per inch of draw roll width for carpet fibers, and lessthan about 200,000 denier per inch of draw roll width for apparelfibers. As the fiber is drawn, the width of the rope may remainsubstantially the same, while the transverse thickness generallydecreases during drawing. Thus, the transverse thicknesses of less thanabout 300,000 denier per inch and less than 200,000 denier per inch willbe understood by one skilled in the art to refer to initial deniers.

The fiber is then drawn in a second stage at a temperature of about 45°C. or more, and up to about 98° or less, under wet conditions. Forexample, as in the first drawing stage, the fiber can be drawn underwater, under dilute finish, under a water spray, or wetted by steam, forexample by a steam jet. The temperature of the fiber during the seconddrawing stage is preferably maintained from about 50° C. to about 95°C., more preferably about 60° C. to about 80° C. Preferably, the fiberis drawn at a rate of 220 yards per minute (ypm) or less. Morepreferably the fiber is drawn at a rate of 100 ypm or less. Too high adraw temperature was surprisingly found to gradually reduce drawability.

The preferred draw ratio depends on the fiber denier and desiredproperties. For example, for 12-20 dpf fibers, it is desired that theundrawn yarn have mechanical draw ratios in the range of 3:1 to 5:1 toobtain useful properties for carpet fibers. It is preferred that thedraw ratio is high enough to obtain desired fiber tenacity and also highenough to allow the fiber to be drawn down to a substantially uniformcross-section. Uniformity of the cross-section of the fiber can bemeasured and quantified using the denier range or standard deviation ofelongation, as illustrated in the present examples hereinbelow. Forexample, it has been found that a draw ratio of about 3.5:1 or greateris desirable in order to obtain substantial uniformity for 14 to 18 dpffibers. Higher spinning speeds or finer deniers result in morestructural orientation, which makes the fiber harder to draw and usuallyrequires lower draw ratios to obtain the same physical properties,including tenacity and elongation. It is highly desired to minimize oreliminate undrawn sections in the fiber, which can be harsh and/orbrittle. The particularly preferred draw ratio for a specific fiber canvary depending on, for example, the intended use of the fiber, and canbe selected by one skilled in the art. For a given denier fiber, aslower spinning speed results in a lesser amount of fiber structureorientation, making drawing easier.

In general, carpet fibers require higher draw ratios than do lower dpftextile fibers because carpet fibers are produced at a lower spinningspeed, which changes the structure of the fibers and lowers the degreeof spin orientation. Thus, higher dpf undrawn PTT carpet yarns requiremore draw orientation than lower dpf fibers. Sufficient orientation isalso required to stabilize the structure of the fiber and obtainadequate, uniform physical properties.

While it has been observed that warming of the fiber alone, for examplewith heated rolls, can provide some improvement in processing andproperties, the present inventors have now found that it is highlypreferred that the fiber be kept wet during all steps of the drawprocess. While it is not intended that the invention be bound by anyparticular theory or mechanism, it is believed that wetting the fibercreates substantially uniform temperatures throughout the fiber due tothe heat transfer capability of water, plasticizes the fiber, and lowersand/or or renders more uniform the forces applied to initiate drawing.Thus, uniform moisture application to each filament is desirable, toachieve sufficiently high fiber orientation, uniformity, and strength.

The relatively slow spin speeds (less than 600 ypm) that may be used inspinning higher dpf fibers, e.g., carpet fibers, on conventionalequipment designed with higher spinneret capillary (also called“spinneret hole”) densities and shorter quench zones (for example, lessthan 16 feet) can result in brittle fibers in such conventionalprocesses. With such equipment, it is generally preferred that thehigher dpf fiber be spun at a speed less than 600 ypm, often about 500ypm or less, even about 500 ypm or less, and in some embodiments about400 ypm or less. For some higher dpf fibers, for example 14-20 dpffibers, spin speeds of about 450 ypm or less, 400 or less, and even 350ypm or less, are appropriate.

The present inventors have found that, for spinning carpet yarn, theprocesses disclosed herein are particularly useful on equipment having acapillary density of at least about 2/cm². Also, for textile yarns, theprocesses disclosed herein are particularly useful on equipment having acapillary density of at least about 8/cm². As will be recognized bythose skilled in the art, for a given throughput of polymer, finerdenier textile fibers are generally spun at faster speeds than carpetyarns and can have higher capillary densities, as the relatively highersurface area of the textile fibers permits faster quench cooling. Forexample, the finer denier textile fibers can be spun at speeds of 900ypm, or even 1300 ypm, depending on the denier.

The processes disclosed herein are particularly advantageous for use onequipment having a quench zone length less than 16 feet. Generally, thelength of the quench zone is at least about 12 feet, although quenchzones shorter than 12 feet can be used. As will be recognized by thoseskilled in the art, a shorter quench zone may require adjustments inother conditions and parameters, such as throughput and speed.

After being drawn, the fiber is crimped. The fiber can be crimped usingany conventional techniques used for PET or nylon fiber such as, forexample, a mechanical stuffer box crimper. In some embodiments in carpetfiber, the crimped fiber has a crimp frequency of 5 or more, preferably6 or more. For carpet, a crimp frequency of about 10 crimps per inch, orless, is generally suitable. For example, in preferred embodiments, a 6dpf carpet fiber has a crimp frequency of about 9 crimps per inch, whilea 18 dpf carpet fiber can have a crimp frequency of about 7 crimps perinch. Generally, for fibers having a lower denier than carpet fiber,such as, for example, for textile uses, it is desirable that the crimpfrequency be up to about 14 crimps per inch or more. The particularlypreferred crimp frequency is dependent upon end use and denier. Finerdenier apparel staple generally requires higher crimp frequencies.

Fibers made according to the processes disclosed herein can be blendedwith other fibers for applications in a variety of textile applications,e.g., for making carpets, and fabrics for apparel and other uses.Blending of such other fibers with polyester fibers, such as those madeaccording to the processes disclosed herein, can provide improvements inphysical properties of the other fibers. Examples of fibers that can beblended with the fibers made according to the processes disclosed hereininclude cotton, rayon, PET, polypropylene, poly(lactic acid), nylon,acrylic, spandex, acetate, wool, and polybutylene terephthalate fibers.

After crimping, it is desired to thermo-fix the fiber with steam tomaximize CTU and provide the needed card sliver cohesion. Thermo-fixingcan be accomplished by applying steam to the fiber, for example, in astuffer box, and heating the fiber to at least about 80° C. andpreferably not higher than about 100° C.

After being thermo-fixed, the fiber is dried, during which time thefiber generally relaxes. Drying can be accomplished by exposing thefiber to heated air at a temperature of about 60° C. or more. However,it is preferred that the fiber is dried at a temperature not exceedingabout 140° C., more preferably less than about 120° C., even morepreferably about 60 to 100° C. With regard to drying, the temperaturesrecited refer to the ambient temperature. It has been found that the CTUis optimized when the fiber is dried at a temperature up to about 100°C. A CTU in the range of about 10% to about 60% is generally desirableand a CTU in the range of about 15% to about 60% is generally moredesirable. A CTU of about 15 to about 45% is preferred for carpet enduses, and a CTU within the range of about 30 to about 50% is preferredfor textile end uses.

The drawn relaxed fiber can be cut into staple fibers having a lengthdepending on the end use in a conventional manner. For example, a staplelength of about 6-8 inches is generally preferred for carpet fibers.

If desired, the fibers can be treated with anti-static agents, whichagents are well known to those skilled in the art. Anti-static agentscan be incorporated into the polymer and/or applied to the surface ofthe fiber. Anti-static agents can be, for example, nonionic, anionic,cationic or amphoteric. The nature and method for using an anti-staticagent depends upon the intended application and the composition of thepolymer, and appropriate anti-static agents and methods for their usecan be determined by one skilled in the art.

The fibers can be used to make a variety of fabrics. Fabrics made fromthe PTT fibers can be, for example, woven, non-woven, knitted, orbonded. Fibers of 6 to 25 denier are suitable for making fabrics andalso for making carpet, using known methods.

For apparel uses, it is generally preferred that the fibers have atenacity of at least about 3.0 gpd (grams per denier, also referred toas “gm./den.”), more preferably at least about 3.2 gpd, e.g., about 3.4or 3.6 gpd or greater. For carpet uses, it is generally preferred thatthe fibers have a tenacity of at least about 2.2 gpd, more preferably atleast about 2.4 gpd.

EXAMPLES

The following examples are intended to illustrate certain preferredembodiments of the invention. It will be recognized by persons skilledin the art that the optimum conditions will depend not only on theequipment and tow size and residence time but also on the desiredbalance between operability and physical properties needed.

Example 1

In this Example, PTT was processed on pilot plant equipment intended foruse for nylon. Undrawn 55 dpf PTT trilobal filaments, having amodification ratio (MR) of 1.65 were produced by melt extruding pelletshaving a relative viscosity (LRV) of 52.0 and an intrinsic viscosity(IV) of 1.04 in a conventional manner at 252-257° C. with a spinningspeed of about 360 ypm, applying a finish, and piddling into a can. Theintrinsic viscosity (IV) was determined using viscosity measured with aViscotek Forced Flow Viscometer Y900 (Viscotek Corporation, Houston,Tex.) for the polymer dissolved in 50/50 weight % trifluoroaceticacid/methylene chloride at a 0.4 grams/dL concentration at 19° C.following an automated method based on ASTM D 5225-92.

Although the fiber was easily drawn as spun, it could not be drawn afteraging as can nylon or 2GT. It became very brittle and had essentially noelongation to break after aging due to storage for a week. This wastotally unexpected based on nylon and 2GT experience as the fiber hadbeen quenched to less than 25° C., well below its glass transitiontemperature (45° C.), and stored at less than 26° C.

TABLE 1 Spinning Conditions for Example 1 Item 55 dpf fiber 8.3 dpffiber Fiber Cross-Section 1.65 MR Round Capillary Cross-Section .000228.0000503 Area, sq.in. Capillary Density, N/cm² 2.46 9.83 Throughput,gm./min/hole 1.87 0.45 Capillary Shear Rate. 6339 9296 I/sec. Spinspeed, ypm 360 560 Jet Velocity, fpm 42.6 46.5 Spun dpf (UDY) 55 8.3 UDYTenacity, gm/den 0.62 1.2 UDY Elongation, % 260 506The 55 dpf fiber, after aging for one week, was drawn under theconditions listed in Table 2, labeled A-1 through A-5.

A finer denier count (8.3 dpf, in Table 1) fiber, having a roundcross-section was also spun. The 8.3 dpf fiber was less brittle and hadbetter drawability than the 55 dpf fiber, but the drawability obtainedwould be unacceptable for some commercial processes. The 8.3 dpf fiber,also after aging for one week, was drawn under the conditions listed inTable 2, labeled B-1 and B-2.

It was found, based on Instron testing, that the initially brittlefibers could be drawn satisfactorily if they were drawn under hot andwet conditions as shown in Table 2. An Instron® Tensile Tester Model1122 was used. The Instron® tester is a high precision electronic testinstrument designed for testing a variety of materials under a broadrange of test conditions. This device can be used for measuring both theforce and the distance required to break either a single filament or amultifilament tow by stretching between two clamps. The bottom clamp isstationary and the upper clamp is moved at a preset speed. A load cellattached to the upper clamp measures the force generated on the tow. AllPTT measurements on this particular Instron were done on yarn in theform of undrawn rope. This instrument has a clamp head speed that can beadjusted between 0.002 and 50 inches per minute.

The relatively slow spin speeds, as shown in Table 1, are suitable fortwo step spin processes for higher dpf spinning with equipment designedfor higher spinneret capillary densities and shorter quench zones (lessthan 16 feet).

TABLE 2 Example 1: Testing on Instron ® Tester, @ 500 mm/min Draw Wet orMax Draw Draw force Item temp., ° C. Dry Ratio variation* A-1 (55 dpf)22 Dry Not drawable — A-2 (55 dpf) 16 Wet 4.5:1 5 A-3 (55 dpf) 38 Wet4.6:1 4 A-4 (55 dpf) 52 Wet 4.6:1 1 A-5 (55 dpf) ~55 Dry 2.7:1 3 B-1(8.3 dpf) 22 Dry   3:1 — B-2 (8.3 dpf) 44 Wet 4.6:1 1 *1 = low drawforce variation: 5 = high draw force variation

Table 2 reports the results of a single draw of fibers of 55 dpf (RunsA1 through A5) and 8.3 dpf (Runs B1 and B2). Both types of fiberexhibited brittleness before drawing. Each type of fiber was drawn wetand dry for comparison. Results reported are maximum draw ratio beforebreaking and draw force variation. Draw force variation, a valueprovided by Instron measurements, is an indicator of uniformity. A lowerdraw force variation (as shown in Table 2, A4 and B2) indicates a lowervariability and is thus desirable.

Although heat alone or moisture alone helped draw the brittle fiber, itwas clear that the most uniform draw was obtained by using both heat andmoisture as evidenced by the draw force variation. When drawn in theabsence of heat and moisture, the fiber had high denier or undrawn harshsections. These results indicate that hot and wet conditions arepreferred to draw PTT fibers and overcome structure changes due toaging.

Comparative Examples (CE2A Through CE2F) and Example 2G

These examples illustrate the properties of PTT processed on commercialnylon melt spun extrusion and drawing equipment. PTT fibers, 40 dpf,1.65 MR trilobal filaments, were produced by melt extruding 52.2 LRVflake in a conventional manner at 266° C., with a spinning speed ofabout 430 ypm, applying a finish, and combining the ends into a spunrope and piddling the rope into cans. The rope from the cans wascombined into a tow and drawn at about 100 ypm in a conventional manner.Drawing conditions are shown in Table 3. Spinning conditions are asfollows: Spin temperature was 265° C.; the spinneret capillary crosssectional area was 0.000228 in²; the capillary throughput was 1.87g/min; the capillary shear rate was 6339 sec⁻¹; the spin speed was 430ypm; the capillary jet velocity was 42.6 feet per minute; the capillarydensity was 2.46 N/cm²; the undrawn yarn temperature was 25° C.; and theundrawn yarn was 40 denier.

The initial conditions tested were with the least aged fiber possible, atwo-hour old very small creel stock, at room temperature withoutadditional water or dilute finish. Even after this short time, the fiberwas not drawable without providing warm and wet conditions in the drawzones (Comparative Example 2A (CE2A)). Modifications to the draw machineto apply hot water with a prefeed kiss roll and spraying hot water inthe drawn zone at about 45° C. permitted operation but gave variableproperties, which is believed to be due to the spray providing onlysurface wetting of a thick bundle. This indicates that more uniformtreatment conditions for each filament, such as wetting under water orsolution, are preferred.

The fiber was initially drawable at up to 2.9× (2.9× its originallength, which can also be expressed as a draw ratio of 2.9:1;Comparative Example 2B) but after 8 hours could only be drawn at 2.5×(Comparative Examples 2C and 2D). The fiber contained harsh undrawnsections as evidenced by the high variations in denier and elongationstandard deviation (S.D.). The fiber was found to be completelyundrawable after about 30 hours due to total bundle breaks, even at thelowest draw ratio possible (2.3:1) on this equipment (ComparativeExample 2F).

The draw conditions used above did not provide adequately uniformtreatment for the filaments or sufficient heat, and also could notovercome draw problems due to aging. These conditions did not provideadequate heat or moisture penetration into the tow. The result wasvariable denier, including some sections that were essentially undrawnand very harsh and brittle. The harsh sections also were found later toproduce excessive fly in carding and harsh carpet fibers.

It was also found that heat setting the drawn fiber in an autoclave at135° C. (Comparative Example 2E) made it much more brittle and reducedthe tenacity from 2.1 to 0.7 gpd. (Such a treatment is common in carpetfiber manufacture to modify physical properties and shrinkage and suchtenacity loss is highly undesirable.) This result illustrates that thefiber structure was also still unstable at these low draw ratios, andthat higher draw ratios to better orientate and stabilize the fiber arerequired.

Drawing the fiber on a modified draw machine with a pre-draw dip tank at45° C. and using a steam jet for the second drawing stage (“Draw 2”)gave acceptable drawability (Example 2G), even after 3 months aging,which demonstrated that the brittle fiber could be successfully drawn to3.9×, with acceptably uniform properties and without any harsh sections.Underwater wetting of a thin band of filaments and heating such a bandgave dramatic improvements over surface treatments. These resultsdemonstrated that effects of fiber aging can surprisingly be reversedand a dry draw machine can be modified for use in producing satisfactoryfiber from PTT.

TABLE 3 Example 2 Drawing Conditions Drawing Conditions CE2A CE2B CE2CCE2D CE2E CE2F 2G Wet or Dry Draw Dry Wet Wet Wet Wet Wet Wet Draw 24 4545 45 45 45 45-50 Temperature, ° C. Draw Speed, 100 100 100 100 100 100100 ypm Draw ratio - 1.8:1 1.8:1 1.8:1 1.8:1 1.8:1 1.8:1 1.8:1 initialpredraw Total draw ratio 2.3:1 2.9:1 2.9:1 2.5:1 2.5:1 2.5:1 3.9:1 Draw2 Steam No No No No No No Yes Jet Time after 2 2 8 16 16 30 3 monthsextrusion, hrs Autoclave, 135° No No No No Yes No No C. Steam aftercrimping Denier & range Not operable 18 Not operable 22/11-32 21 Notoperable 11 Tenacity, gpd 2.2 2.1 0.7 3.4 Elongation, % 64 167 82 71Elongation %, 13 56 6 std. deviation

Example 3

This example demonstrates drawing of the aged brittle 55 dpf undrawnyarn of Example 1 under a series of processing conditions. Results areshown in Table 4. The draw machine was capable of single or two stagedraw, prewetting the fiber in a dip tank, drawing under water or dilutefinish in the first stage (“Draw 1”), and drawing in the second stage(“Draw 2”) under hot sprays or with a steam jet over a range oftemperatures in these zones. The draw/crimp zones were coupled to adryer, and the drawn fiber could be crimped and relaxed/dried over arange of conditions. The equipment used for these trials is shown inFIG. 1.

The UDY produced in Example 1 was drawn, crimped, and relaxed asdescribed below. The processing conditions allowed the fiber to be drawnat up to 5.6×, instead of being essentially undrawable as on the nylonequipment described in Example 2, with much better properties and noharsh undrawn sections, even after lagging the fiber for 60 days.

The predraw dip tank was found to improve draw uniformity. As shown inExamples 3A and 3B, excessive heat can crystallize the fiber and reducedrawability and operability due to broken filaments. A single draw stagegave satisfactory operability at up to 3.3× with the prefeed dip tankand dip draw and fair performance at 3.6× (Example 3A).

Two draw stages gave improved drawability. Example 3C showed that a 4.5×was obtainable with more draw taken in the second stage i.e. a higherpercentage of the total draw in the second stage than in the first stage(40% in Draw 1 and 60% in Draw 2). However, if more draw was taken inthe first stage, (56% in Draw 1) a 5.5× draw was feasible (Example 3Fshows properties at 5×).

It was found that too high of a temperature in the first draw stage (90°C.—Example 3E) did not provide as good operability as did a first drawstate at 50° C. (Example 3F) and reduced the maximum draw ratio,presumably because of excessive crystallization. The best performancewas observed under the conditions used in Example 3F indicating lowertemperatures are better than high.

TABLE 4 Example 3: Optimizing Drawing Conditions Item A B C D E FPredraw, ° C. 22 85 22 22 22 22 Draw 1, ° C. 50-90 90 50 90 90 50 Draw2, ° C. off off 98 60 60 60 (Draw 1)/(Draw 2) 3.6/1 3.6/1 1.8/2.52.3/1.8 2.9/1.4 2.8/1.8 Total Draw Ratio 3.6:1 3.6:1 4.5:1 4.2:1 4.2:15.0:1 % Draw 1 100 100 40 55 69 56 Draw speed, ypm 50 50 50 50 50 50Operability Fair Poor Good Good Fair Good Denier 12.7 13 Tenacity,gm/den 3.6 3.8 Elongation, % 52 52

Example 4

This example demonstrates another surprising effect found with PTTfibers: varying the thermo fixing of the fiber after crimpingsignificantly affected both downstream processing operability and carpetbulk to a surprising degree based on nylon and PET experience. The samespun fiber as in Example 2 was converted to carpet tow on the equipmentshown in FIG. 1 and was cut to a length of 6 inches. The staple was thenconverted into yarn on conventional modified worsted equipment. Thefiber was ring spun into 3.25 cc with 5.1 t.p.i. and was plied to 4.9t.p.i., and Suessen heat set at 200° C. It was then tufted into a ⅛ ga.,50 oz./sq.yd, with ⅝ inch pile height. The carpet was then disperse dyedon a continuous dye range and finished in a conventional manner.

Example 4A shows that without steam assist in crimping the fiber had alow CTU. In mill processing, the card sliver had a very low cohesion,even though the crimp frequency was similar to the other items, andcould not be carded as the sliver pulled apart. Example 4B shows thatwith steam assist the process becomes operable and both the CTU andsliver cohesion are improved. Example 4C shows that lowering thedryer/relaxer temperature from 165 to 60° C. not only significantlyimproved the CTU but also improved the carpet bulk.

TABLE 5 Example 4: Tow Preparation and Carpet Yarn Evaluation Item A B CSpun dpf 40 40 40 Total spun denier 212480 212480 212480 Draw ConditionsPrefeed, ° C. 22 22 22 Draw 1 , ° C. 50 50 50 Draw 2, ° C. 50 60 60 Drawspeed, ypm 49 75 75 Draw 1/Draw 2 1.8/1.7 2.2/1.7 2.2/1.7 Total Drawratio 3.1:1 3.6:1 3.6:1 Crimping Conditions Roll Pressure, psi 25 20 20Gate Pressure, psi 46 32 32 Steam Pressure, psi 0 15 15 RelaxerTemperature, ° C. 100 165 60 Relaxer Time, min. 6 6 6 Staple Denier 14.913.1 13.5 Tenacity, gpd 2.3 2.4 2.4 Elongation, % 107 81 90 Boil-offShrinkage, % 2.4 0.2 1.8 Dry Heat Shrinkage@196° 8.5 5.9 9.3 C., % CrimpFrequency, cpi 7.6 6.8 6.9 CTU 8 13.5 39 Finisher Sliver Tenacity,Cohesion too low to 1.3 2.1 gms./grain card Relative Carpet Bulk NA 0+10%

1-30. (canceled)
 31. A poly(trimethylene terephthalate) textile staple fiber of 1 to 6 dpf, having a tenacity of at least about 3.0 gpd and a crimp take-up from about 15% to about 60% wherein the staple fiber is prepared by a process comprising: prewetting a undrawn yarn consisting essentially of poly(trimethylene terephthalate) at a temperature less than about 45° C.; drawing the fiber under wet conditions at a temperature of from about 45° C. to about 95° C. in a first stage to a length of about 30 to about 90 percent of its final length; drawing the fiber in a second stage at a temperature from about 45° C. to about 98° C. under wet conditions; crimping the drawn fiber; thermo-fixing the crimped fiber in the presence of steam at a temperature from about 80° C. to about 100° C.; and drying the crimped fiber at 60° C. to 140° C.
 32. A poly(trimethylene terephthalate) carpet staple fiber of 6 to 25 dpf, having a length of about 6 to 8 inches, a tenacity of at least about 2.2 gpd and a crimp take-up from about 10% to about 60%.
 33. A 6 to 20 dpf poly(trimethylene terephthalate) staple fiber according to claim
 32. 34. A poly(trimethylene terephthalate) fiber of claim 31 wherein said tenacity is 3.2 gpd or greater.
 35. A poly(trimethylene terephthalate) fiber of claim 32 wherein said tenacity is 2.4 gpd or greater.
 36. An apparel poly(trimethylene terephthalate) fiber of claim 31 wherein said crimp take-up is from about 30% to about 50%.
 37. A carpet poly(trimethylene terephthalate) fiber of claim 32 wherein said crimp take-up is from about 15% to about 45%.
 38. A yarn prepared from a fiber of claim
 31. 39. A fabric made from a yarn of claim
 38. 40. A textile or non-woven fabric of claim 39 further comprising one or more fibers selected from cotton, rayon, PET, polypropylene, poly(lactic acid), nylon, acrylic, spandex, acetate, wool, and polybutylene terephthalate fibers.
 41. A yarn prepared from a fiber of claim
 32. 42. A carpet, rug or nonwoven fabric prepared from a fiber of claim
 41. 43. A carpet, rug or nonwoven fabric of claim 42 further comprising one or more fibers selected from cotton, PET, polypropylene, poly(lactic acid), nylon, acrylic, wool, and polybutylene terephthalate fibers.
 44. A fiber according to claim 31, comprising an anti-static agent.
 45. A fiber according to claim 32, comprising an anti-static agent. 